A novel Positron Camera using lead converters and gas filled multiwire proportional chambers has been constructed under N.S.F. support. This sensitive low cost system produces images of distributions of positron emitting radiopharmaceuticals with intrinsic tomography. It is proposed that this system be applied to Brain imagng in patients with malignant brain tumors being treated by chemotherapy under an N.I.H. contract, number 14093-02, from the NCI. Seventy-five patients will be studied prospectively. Each undergoes repeated multifactorial evaluation of response to therapy including clinical outcome, electroencephalography, computerized axial x-ray tomography, and conventional brain scintigraphy. Positron brain scans using 68Ga DTPA will be added to this evaluation, and periodically compared to the other modalities. Preliminary data suggests that positron imaging may be the best single modality in assessing response of brain neoplasms to chemotherapy.